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Aptose finally ditches APTO-253 after 3-year clinical hold, phase 1 dud

The writing was perhaps on the wall for this one back in 2018: Aptose Biosciences has decided to end clinical development of the c-Myc inhibitor APTO-253, a therapy that was the subject of a three-year FDA clinical hold.

In a brief update Monday morning, Aptose said that APTO-253’s journey through the clinic is officially over. The biotech will turn now to developing its two other pipeline assets, including kinome inhibitors HM43239 and luxeptinib.

Those two therapies have shown encouraging data in hematologic cancers, according to Apstose Chairman, President and CEO William Rice, Ph.D.

The decision to ditch APTO-253 comes after the prioritization and an internal review of the product profile—including that FDA clinical hold, the company said.

RELATED: After nearly 3 years, FDA lifts hold on Aptose cancer drug

“APTO-253 remains an interesting product that has demonstrated MYC repression, which creates optionality across the wider oncology spectrum. Moving forward, we plan to explore available strategic alternatives for this compound,” Rice said.

Trouble with APTO-253 arose back in 2015, when a phase 1b study in patients with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) was halted following a report of a problem with an infusion pump. Aptose then discovered irregularities with the manufacturing documentation and a solubility problem. It took three years to get the study back on track.

Aptose had been aiming to prove that APTO-253 could help in treating various types of cancer by inducing cell death through the inhibition of the oncogene c-Myc, which is involved in cell growth and metabolism.

But at the American Society of Hematology meeting earlier this month, the biotech reported that APTO-253 did not induce a clinical response in the phase 1 AML and MDS study.

RELATED: Aptose signs $125M-plus BET inhibitor deal with Ohm Oncology

Shares of Aptose were trading down 5%, dropping to $1.42 apiece as of 11:35 a.m. ET on December 20.

RBC Capital Markets analysts said the discontinuation news is clearly negative for Aptose, but the asset was “lagging.” The lead programs, luxeptinib and recently acquired HM43239, are the bigger stars of Aptose’s portfolio.

“We believe 2022 is shaping up as an important show-me phase for Aptose in order for investor appreciation to manifest, especially as the company’s cash runway into early 2023 re-enters the conversation,” RBC said in a Monday morning note.

HM43239 is undergoing a phase 1/2 trial in relapsed or refractory AML. Luxeptinib is being tested in two phase 1 a/b studies: the first is in those with relapsed or refractory B cell malignancies who have failed on other treatments, while the second will include patients with relapsed or refractory AML or high-risk MDS.

Annalee Armstrong

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